GCSE Science (Biology) Asexual Reproduction Sexual Reproduction Inheritance DNA Chromosomes Genes

1. Cell Division and Inheritance

2. Cell Nucleus
Chromosomes
DNA
Genes
Amino Acids
Proteins

3. Chromosomes- Threadlike structure, composed of DNA and a
protein, that form in the nucleus when the cell begins to divide and that
carry the genes which determine an individual's traits.
 They come in pairs.
 Every nucleus contains 23 pairs.

4. DNA-Complex chemical that contains the genetic information
for Cell Growth, Division and Function.
It controls-
 Hair Colour
 Eye Colour
 Height
 Face Shape
 Intellegence
 Blood Type
PRETTY MUCH EVERYTHING!!

5. Genes- Short sections of DNA.
Each gene has a specific purpose. It has the instructions for
making a particular amino acid. The amino acids then join
together to form proteins.

6. Asexual reproduction- Reproduction without the
sexual union of male and female gametes.
Mitosis- Cells divide into two. These two new calls contain the same
DNA as the origional one and so are identical.
Asexual reproduction is a 5 step program-
1. Take a parent cell.
2. The chromosomes make identical copies of themselves.
3. The chromosomes line up in the centre.
4. The copies serarate and move apart.
5. The cells split into two. Each cell has a copy of the origional cell's
DNA.
This happens again and again to produce lots of identical cells.

7. Asexual reproduction-

8. Sexual reproduction- Reproduction by combining
genetic information from two different sexes.
Meiosis- Production of special cells called Gametes (Sperm and Egg) . This only
happens in the reproductive organs.
How does Meiosis work?
The 23 chromosome pairs start copying themselves and double up. Then,
sections of DNA get swapped between similar chromosome pairs. This
swapping is where the genetic variation comes from. The call then divides into
two and then them two both split again so there's four cells each containing
23 chromosomes.
 Each pair of chromosomes is split so that each sperm and egg cell only
contain 23 single chromosomes.
 The male and female gametes then join together and their single
chromosomes join up to make 23 pairs. This newly formed call contains a
unique mis of chromoomes from each parent. This is called fertalisation.

9. Sexual reproduction-

10. Comparison of Asexual and Sexual
reproduction-
Asexual Sexual
Pro
Con
• High genetic variability.
• Helps adaption.
• "Speeds" up evolution.
• Saves energy.
• There's no need for 'Hanky
Panky'.
• Needs a lot of energy.
• 'Hanky Panky' is time and
resource consuming.
• Low genetic variability.
• Adaption to environment
is difficult.
• Decelerates evolution.

11. Inheritance- Genetic characteristics transmitted from
parent to offspring.
 Different forms of the same gene are called Alleles. For
example- The gene for eye colour has an alele for blue eyes
and an allele for brown eyes.
 Alleses are either Domninant or Recessive. In eye colour the
brown allele is dominant to the blue allele. This means that if
there were a blue and brown allele present the child would
have brown eyes.
 Genetic diagrams-
 The rule is to use a capital letter to represent the dominant
allele and a lower-case letter for the recessive.

12. Example of how a child can have blue eyes
when both parents have brown-
Brown is dominant so is represented by a 'B'.
Blue is recessive so is represented by a 'b'.
Bb Bb
Bb Bb
B Bb b
bbBB

13. Sex chromosomes-
 Male- XY
 Female- XX
 The sex chromosomes pair determine whether you are male or female.
 Gametes only contain one sex chomosome. This means that all egg cells must
contain an X where as sperm could either contain an X or Y chromosome. If the
sperm cell contains the Y chromosome then the baby will have XY and be male and
so if the sperm cell contains an X chromosome then the baby will have XX and be
female.